Breakdown: The ice in my drink is white, so why is Black Ice on the roadways clear and difficult to see?

Published: Jan. 2, 2022 at 10:36 AM CST|Updated: Jan. 2, 2022 at 11:00 AM CST
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MEMPHIS, Tenn. (WMC) - It’s officially winter, and now that the weather has gotten chillier, it does bring some challenges with it, such as black ice.

The National Weather Service defines this as “patchy ice on roadways or other transportation surfaces that cannot easily be seen.”

To the human eye, it’s all but invisible. Black ice isn’t really black; it’s transparent. The stuff only looks black when it’s covering a layer of jet-black pavement. Accidents happen once drivers, blind to the danger, steer their cars over the ice and lose traction.

Other kinds of ice are easier to see. You’ve likely noticed that homemade ice cubes usually look cloudy and opaque.

So, how come black ice is see-through, but the cubes in your typical ice trays aren’t?

Technically, water isn’t colorless (although it often looks that way). Believe it or not, the liquid has a natural bluish tint, owing to the fact that it absorbs red, yellow and orange light more easily than blue light.

But our human eyes can only observe this indigo quality in deep bodies of water, which explains why the ocean looks blue to us while glassfuls of drinking water look transparent.

It’s also why big, thick glaciers adopt a royal hue. That’s because the material does not absorb most of the visible light that passes through it.

A view of the blue ice of Pedersen Glacier at its terminus in Pedersen Lagoon (Kenai Fjords...
A view of the blue ice of Pedersen Glacier at its terminus in Pedersen Lagoon (Kenai Fjords National Park, Alaska)(National Park Service)

Additionally, there’s a deceptive quality to water: No matter how fresh it may seem, it’s never 100% pure.

A sample of water might contain floating bits of organic matter — algae, plant remains, etc. — along with suspended sediments, dust particles or flecks of minerals like calcium and lime.

It also harbors lots of dissolved gases, such as oxygen, because without oxygen, fish wouldn’t be able to breathe.

These gases and physical impurities are the key to understanding why those ice cubes in your lemonade pitcher are cloudy.

Memphis Ice Machine Company says, “ice that comes out of a kitchen ice machine or ice cube tray is usually white or cloudy in the middle. The reason this happens is because when water is put into a tray and left to freeze, it freezes from the outside in. The first thing to freeze is the cleanest, purest water—which means air bubbles, minerals and impurities get pushed towards the middle of the cube. That’s what causes the cloudiness.”

To make clear ice cubes, you should first boil the water.  Boiled water has much less dissolved...
To make clear ice cubes, you should first boil the water. Boiled water has much less dissolved gas that can cloud up the ice.(Memphis Ice Machine Company)

Additionally, ice is made up of crystals, and when water freezes rapidly, those crystals tend to be small and numerous -- which makes the ice look whiter because crystals have reflective surfaces.

On the other hand, ice that’s been slowly frozen has fewer and larger crystals -- which promote transparency.

This is where black ice comes into play.

Black ice always freezes slowly and during low-wind periods. It’s consistently thin and it contains very few impurities and almost entirely free of air bubbles. That’s why black ice is so transparent.

So, to recap, ice will only become see-through and crystal clear if it freezes slowly and doesn’t have too many impurities or crystals.

Prevent or minimize future encounters with black ice

There are several things that you can do to reduce the chances of being surprised by black ice. While knowing how to drive on it remains a number one priority, here are some other things to do, according to the United States Forest Service:

• Travel slowly. Don’t try to speed during icy weather as this will take away any control you might have had on the black ice.

• Don’t tailgate.

• Keep your windshield clear of ice, snow, dirt, and anything else that can prevent you from seeing out of it properly. To get snow and ice off the windshield of your car, you might be tempted to turn on your windshield wipers. It might seem like the wipers and the washer fluid will work, but they don’t. In fact, if you use your windshield wipers to get ice off the windshield, you could ruin them. Use an ice scraper to scrape the ice from the windshield of your car before starting the vehicle.[9]

• Turn your headlights on early in the afternoon to help you see any possible sheen from black ice.

• Check your tire tread. Worn tread causes accidents in any conditions, and will ensure you lack traction when needed on black ice. In addition, consider having snow tires fitted.

• An important thing to remember is to NEVER drive in potentially icy conditions with your cruise control active. Tips

• If you have ABS brakes, know how they feel when they engage so you don’t panic and that you understand what denotes slippery conditions– even if your car is still in control.

• Walking and cycling on black ice is also dangerous and can cause you to slip. Cyclists need to take extra care as slipping can lead you into the pathway of car and truck traffic.

• Have snow tires fitted before the temperatures drop low enough to cause black ice. This is especially important if you’re traveling outside your urban areas and you’re not familiar with the roads and weather conditions.

• Stay off of the phone, and don’t mess with the radio. Pay attention to the road or you might wreck!

• A good tip for any ice driving is to avoid sudden movements. Quickly turning your tires, accelerating or braking can cause you to lose traction. One way to adapt your driving style to winter travel is to imagine an egg between your foot and the gas and brake pedals. Make it a priority to keep the imaginary egg intact. You’ll find yourself driving more cautiously in no time.

• If the weather is bad and the conditions are likely to result in black ice, try to stay home and avoid driving at all.

https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fseprd488148.pdf

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